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The Future Is Now: The 2007 A/C Report

New SAE standards, and a bevy of new equipment designed to meet them, will improve a/c service accuracy, reduce refrigerant waste and (possibly) delay the need to introduce an R-134a replacement with a lower global warming potential.

Vehicle air conditioning systems have been under the overall control of the powertrain computer for years, but actual service of the refrigeration circuit has been akin to changing breaker points and condenser. In recent years MOTOR has been talking about changes on the horizon, and the need to introduce high-tech precision to servicing a/c systems.

Well, we're now at the horizon. The first new SAE standard�J2788�was issued at the end of December 2006, and it's spawning a generation of recover/recycle/recharge equipment that complies. The first machine, from SPX/Robinair, was shown and demonstrated at the 2007 MACS convention and trade show in Phoenix. All other leading manufacturers told MOTOR they're making arrangements with EPA-listed laboratories to get their new machines approved. You'll shortly have a wide choice. And although J2788 makes it possible for manufacturers to produce recover/recycle-only or recharge-only equipment, the overall requirements of the standard dictate that an R/R/R machine is what you'll be seeing, at least for the present.

The new machines must remove at least 95% of the refrigerant, tested against a 2005-07 Chevy Suburban with rear air�a 3.0-lb. system�in no more than 30 minutes at 70°F ambient. There are lots of smaller, easier-to-evacuate systems, to be sure, and on those, a J2788-compliant machine will be a speedy sensation. It's not just speed. The J2788 machines also must measure and indicate the amount of refrigerant removed�accurate to 1 oz.�as compared with a simultaneous reading on an ultra-precise laboratory scale. And if the machines also recharge, they must do that even more accurately�to within 1 /2 oz. And that degree of accuracy must be something you can check in the service bay, not have to call the equipment maker's service rep to do for you.

Do you really need that level of precision and recovery speed? Yes, because although we're still using R-134a, vehicle a/c systems have undergone major changes.

Charges and Tolerances Have Come Down

The old R-12 and early R-134a systems had 50 oz. of refrigerant, some even more. Recovery and recycling was legally mandated from the start of the R-134a era, and an SAE standard for recovery and recycling equipment�J2210�came into effect. We thought that would solve all the problems.

But refrigerant charges have come way down. Condensers and evaporators are much smaller, have multiple-flow mini-paths and hold much less refrigerant, but are far more efficient, so performance is still good. The big receiver-dryers that held so much spare refrigerant are gone, replaced by a thin-pipe so-called integrated modulator at the side of the condenser. Today's systems are so much tighter that unless there's a significant leak, they can go five years or more with the original charge.

However, as refrigerant charges have come down�they're now as low as 12 to 14 oz.�the charge tolerance also did, typically no more than 10%�just over 6.5 oz., and in some cases even less (BMW is 1 /3 oz.). The old equipment was a clunky antique when used with these smaller charges. If your machine reads to .1 lb. (1.6 oz.) or 1 oz., shouldn't that be close enough to avoid trouble? The answer is, don't be misled by the resolution of the display. It doesn't mean that the scale (or other device) actually is anywhere near that accuracy. The deluxe machines of not long ago had actual scale accuracy�when brand new�of 6.2 lb.�a total of about 6 1 /2 oz., even though the digital display read out to .l lb. or 1 oz.

Even the more recently produced recover/recycle machines, which far exceed J2210, wouldn't recover almost all the refrigerant in a single, quick operation and, after recycling, charge the small system with a precision that the vehicle makers said was critical. A/C performance problems from an incorrect charge have become a routine issue, with some technicians trying a variety of methods, but nothing with the accuracy needed.

J2210 didn't even mention recharging accuracy, so whatever you use to install refrigerant meets absolutely no standard for accuracy�whether it's a charging cylinder, a scale, whatever�even if built onto a machine that meets J2210. J2210 simply said the machine's recovery compressor had to pull down to 4 in./Hg vacuum, not particularly meaningful when it's sucking through the restriction of a service valve.

How much refrigerant did an old machine actually pull out? Our best estimates are maybe half�even less with poorly maintained equipment with clogged filters. Tests with brand-new premium J2210 machines, pulling more than double the J2210 requirement, and on a front-only a/c system, would recover less than 85% at 70°F and less than 70% at 50°F�not good enough.

If more than 15% to 30% of the refrigerant is left in the system and it's recharged (by pure luck) to specs, the system is overcharged 15% to 30%, which translates to excessive high-side (“head”) pressures. In hot weather, the compressor will run hot and the clutch may slip. Sure, you can run the vacuum pump for an hour, and if it happens to have been well-maintained, the machine may get most of the remaining refrigerant out, venting it to the atmosphere. But that's a waste, and the environmentalists don't like it either.

The 95% recovery spec wasn't pulled out of thin air. Some refrigerant is trapped under the oil and/or is mixed with the oil in the system, but experimentation found that a powerful recovery compressor could reach 95% quickly. That means that even if a technician just runs a vacuum pump for perhaps 6 to 10 minutes, he'll get out any air. And if he recharges to the midpoint of the factory specs, which is possible with the accurate scales in the new machines, the charge should be pretty well right on.

Getting out at least 95% of the refrigerant and then running a brief deep vacuum to remove air is faster, saves money on refrigerant and, if you then charge accurately, gives better results. So although you can legally continue to use your existing recover/recycle machine, it's not cost-effective.

With a J2788 machine, you'll probably save 50% on your refrigerant expenses and at least 30 to 45 minutes on each job, plus you'll reduce comebacks from incorrect charging. Even if you're accustomed to letting your vacuum pump run 30 to 45 minutes to get out the refrigerant the old recovery machine didn't pull out, you still may leave in more than you'd expect. In testing for J2788, it took a four-day procedure (four separate pulls with the recovery compressor), using a premium J2210 machine, to remove 95% of the refrigerant charge. And although you likely would do better with a very good, well-maintained vacuum pump, we wouldn't bet on a half-hour with the typical vacuum pump. A typical pump probably hasn't had an oil change in much longer than the every 10 hours it should get to be able to pull a deep vacuum. A lot of refrigerant can be trapped in the nooks and crannies of a modern system, and a weak pump won't remove it.

Also, the speed of the new J2788 machines means that you can even use recovery and recharge as a diagnostic tool, if a poorly performing system had been recharged elsewhere.

The Robinair machine is a somewhat different design than has been used in the past. The vacuum pump is in series with the recovery compressor. During refrigerant recovery, the compressor pulls down to zero pressure, then the vacuum pump continues to pull�through the compressor�to continue recovery and bring the system into deep vacuum. So if the system hasn't been left open, no separate vacuum pump operation is needed at all. If it is left open (especially in a humid climate), Robinair recommends 15 minutes of vacuum pump operation.

Scale accuracy of the J2788 machines will not only save refrigerant by avoiding overcharging, but also will save compressors from failure caused by undercharging. Just a few ounces under specs on a small system not only reduces high-ambient-temperature a/c cooling performance, but the oil circulation that lubes the compressor.

And down the road�in fact, at any time�you can check the accuracy of the scale on that new machine, because SAE J2788 requires an in-shop procedure. If it's a scale, that almost surely means that you get a calibration weight. (Robinair supplies a ball bearing that adheres magnetically to the underside of the scale. Hit the right buttons and the Robinair machine's computer runs a scale calibration check.)

The scale is a precision instrument, so the machine should be treated with reasonable care. That means no rolling it into a wall to get it out of the way. However, the J2788 certification test does require the scale to hold its calibration�with no scale readjustment allowed�during immediate testing on the Suburban a/c system after being rolled quickly across the lab's shop floor. But treat it the same way you'd handle an oscilloscope or similar shop equipment, not the way you handle a box wrench.

Of course, any recover/recycle machine's recovery performance would drop significantly with a plugged filter, but that won't happen with a J2788 machine. The machine must monitor the filter and give repeated warning displays as the filter reaches end-of-life, to give you lots of time to get a replacement. With a plugged filter the J2788 machine eventually will stop, but installing a replacement filter, entering the code number on the label and hitting reset will restart it.

With vacuum pump-assisted recovery, pump maintenance is important. As a result, the digital display issues a “change pump oil” notification every 10 hours of pump operation (the industry-recommended maintenance interval).

Air drawn into the machine with recovered or recycled refrigerant must be purged from the tank or it will be another cause of poor performance if charged into a vehicle's a/c system. J2788 not only requires an automated air purge, but another method as well (perhaps a computer algorithm) that allows enough time for air-refrigerant separation to have occurred (air rises to the top), to minimize loss of refrigerant.

Many shops have machines with manual air purge, in which they have to compare recycled refrigerant tank pressure with ambient temperature. If the pressure is high enough to indicate air in the tank, the tank vent valve must be manually opened to let it out. The details are outlined in the machine's instruction manual, but when was the last time anyone in your shop actually did that kind of purge? With this new assurance of air-free refrigerant, a J2788-compliant machine gives you still another feature that ensures good results from a recharge.

Machines certified to J2210 legally may be sold until the end of this year, but if you're going to invest, make sure your choice meets J2788. We've been to many shops, and even to repair facilities that service recover/recycle/recharge equipment. We've seen machines that were badly abused, with filters that had never been changed, service hoses that were cracked and taped over and O-ring seals in the ends that were in even worse shape. Such mistreated machines will suck in a lot of air to mix with the refrigerant. If you don't want to service a/c systems with the new equipment that's needed for today's small-charge systems, you'll probably have more satisfied customers if you send them to a specialist who's ready and willing to do it.

However, if you know a lot of shops that are using and abusing old machines they won't replace, start upgrading your a/c equipment and be the guy that eventually gets the jobs these shops are not doing right.

What About System Leakage?

We said that the new systems are so much tighter that they can go five years without a recharge. But what if they don't? What if they lose just a couple of ounces of refrigerant a year from a few leaks that used to be considered “normal”�but enough to really affect cooling with the small charge systems? A good older compressor may leak .5 oz. per year, vs. some of the advanced new designs that have minuscule loss�maybe under .2 oz. per year. The new joints are almost leak-free when they're in good condition, but what if they leak close to .5 oz. per year? Those leak rates are at the edge of what today's premium electronic leak detectors are designed to find.

That's a problem, and we won't sugarcoat the situation. Trace dye still works, but there's no way to predict the size of the leaks it detects in any particular situation. (The trace dye manufacturers have tried to help technicians determine leak size; it's not a simple situation.) If the system contains trace dye, great; check around with an ultraviolet lamp. If it doesn't contain dye, you can inject a dose and send the customer out to circulate it through the system, with the hope that when he comes back, traces of dye will show.

That's not a prescription for happiness in a hot spell, so you should check for leaks with a well-maintained premium model electronic detector. If you move a premium detector slowly along the refrigeration circuit, encircling all joints (including switch ports), it often will detect a smaller leak than the nominal .5-oz. rating. At the service valves, the caps are the primary seal, and if the O-rings inside are missing (or certainly if the caps are gone), that's a problem area. Clear the area of each valve with shop air, thread on the cap, wait a few minutes, then recheck with the detector.

Oh, you say you hate electronic leak detectors because they all false-alarm? It's not a simple subject. Alcohols (particularly washer fluid) and some other underhood chemicals trigger detectors, and there are limits to reducing the problem. Wipe the circuit clean; don't use aerosol cleaners, most of which are in the class of chemicals that will cause false triggers. Underhood fumes are another problem, so clear the area with shop air first.

A new SAE standard (J2791) has been approved for next-generation leak detectors. But it's fresh off the presses and no detectors have been certified as of this writing. The document specifies detection of far smaller leaks (down to 1 /7 oz. per year), as well as operation in an underhood area contaminated by fumes. But until there are detectors that meet the standard, we have to make do with what's available.

Finding evaporator and compressor shaft seal leaks is a tough problem, but an SAE work group is testing different methods. Ultimately, it will incorporate them in a revision of J1628, a standard that covers techniques for tracing leaks.

For the present, trace dye is popular for evaporator and shaft seal leak detection. However, even with trace dye for an evaporator, you have to look up the condensate drain. Using a borescope with a mirror and UV light is the best approach, but only if there's access to the drain. (Some Mercedes models have four drains, so good luck on that one.) And if there's a buildup of debris on the evaporator, trace dye may just soak in, so even with a borescope, the job may be no picnic.

Many shops also find shaft seal leaks by running the system with the radiator electric fans disconnected or the condenser blocked, to kick up high-side pressures. They shut the engine and, during system equalization (when low-side pressures go up), look for an electronic leak detector to trigger at the compressor nose and at the bottom of the clutch in the gap. They may get an alarm, but not know how big the leak is. Unless you know it's large (and this method doesn't tell you), replacing a compressor could be an expensive mistake.

Well, now you know why we don't always have great answers. The annual MACS convention tries to give a/c service techs the latest, best information available. So come on down (to Orlando in 2008) and sit through some tech sessions.

Paul Weissler was the technical discussion leader of the SAE work group responsible for creating the J2788 (a/c recover/recycle/recharge) and J2791 (electronic leak detection) standards.